English and Scientific names:

Thayer’s Gull (Larus thayeri)

Number of individuals: 

One first-cycle in prealternate molt

Locality: LOUISIANA: 

Jefferson Davis Parish

Specific Locality:

Jefferson Davis Parish Sanitary Landfill, ca. 2.5 mi. NW of Welsh

Date(s) when observed:

28 February 2009

Time(s) of day when observed:  

~10:15-10:30 AM CST


Reporting observer and address:

Devin Bosler

Baton Rouge, LA 70802

Other observers accompanying reporter who also identified the bird(s):

Justin Bosler

Other observers accompanying reporter who also identified the bird(s): 


Light conditions:

Overcast sky with fair late morning sunlight.  Backlighting or glare not a factor.

Optical equipment: 

Zeiss Victory FL 8x42, Nikon Fieldscope w/ 20-60x optical zoom, Canon Powershot SD1100 IS (all equipment in good condition)

Distance to bird(s): 

ca. 75-100 meters

Duration of observation:

~15 min.


Rural, sanitary landfill surrounded by open, aquaculture wetlands, ag. fields, and livestock pastures.

Behavior of bird: 

The gull was observed in flight, foraging, and at rest.  It was only one very few large, white-headed gulls in first-cycle plumage.  It was scavenging and picking at scraps of trash on the east slope of the open pit among thousands of Ring-billed and Laughing Gulls.  There were only about fifteen American Herring Gulls present at the time of observation, perhaps 50/50 ad./imm.  Strong, gusty north winds made photo-documenting a challenge.  Operations supervisor advised us not to take any additional photos.



A medium-sized gull with frosty, neatly-patterned brown upperparts and smudgy brown, mottled underparts.  Juvenal scapulars being replaced giving smudgy, contrasting appearance to upperparts.  A relatively steep forehead, giving the bird a delicate, round-headed appearance.  Long-winged with medium-dark brown wingtips with conspicuous pale edging on primary tips.  Pale silvery undersides to primaries, dark brown secondary bar, and broad dark tail band (when observed in flight).  Distinctive, two-toned outer primaries (pale inner webs and dark outer webs) were visible on spread wing.  Evenly barred undertail coverts.  Relatively slender blackish bill with some dull flesh at extreme base, bleeding onto rami.  Short, deep pink legs and feet.  Dark irides. 



No vocalizations heard.

Similar species:

First-cycle American Herring Gull (AMHE) can be eliminated by the overall smaller size (larger than RBGU but smaller than accompanying AMHE), slender bill, and short legs.  Wingtips medium-dark brown, not black as in AMHE.  Pale edging on primary tips diagnostic for THGU.  Frosty upperparts unlike AMHE.  Structurally unlike AMHE with steep forehead, round head, and potbelly.  First-cycle Kumlien’s Iceland Gull (KUGU) can be eliminated by the overall larger size, smudgy brown plumage, dark-centered tertials, relatively large bill with noticeable gonydeal expansion, long wings, dark secondary bar, and broad dark tail band.  KUGU are small, very pale, short-winged gulls. 

Photographs or tape recordings obtained?

Yes, digiscoped photos by Devin Bosler.  Yes, attached. 

Previous experience with this species?

Previous experience with THGU from a single first-cycle individual self-found at MacMillan Wharf in Provincetown, MA (Barnstable Co.)  on 21 Dec 2006, accepted by MARC as fifth well-documented state record. 

Identification aids: 

at time of observation:


after observation:

National Geographic Complete Birds of N.A. (Alderfer et al. 2005), and Gulls of the Americas (Howell and Dunn 2007).

Notes made from? 

notes made during the observation , notes made after the observation, memory.

Are you positive of your identification? If not, explain: 


Yes, very confident.


Devin Bosler 

Date and time: 

4 March 2009 

6:00 PM CST